Just do it between meals I usually use applecider vinegar in water, because I don't want all the calories and sugar, but you might not care.
5 years ago I bought the malic acid from a winemaker, but I could not take it, it was so sour. It was at that time difficult to find malic acid tablets without other ingredients added.
Don't worry too much about it the flush will still work.
It is good that storm has passed and I am out of the news :)